I'm in Japan at the moment and paid a visit to the Ricoh/Pentax offical showroom in Shinjuku (Tokyo). Had a play with the K-1. It's there and its real! Very solid feeling and focusing with the new DC motors very quiet and confident (mostly played with the new 28-105). Mirror is distinctly quick and very quiet. They're done a very good job with that. This immediately stood out, even vs the K-3 I use. Putting lenses aside, the handling of the K-1 was very similar to the K-3. The man there would probably sell me one later this week but unfortunately I need to pay off the Japan trip (for 4 people) first
Also sighted the new DFA 15-30 and had a quick play with it on the K-1. Broadly similar size to the 24-70.
Both it and the 24-70 are solid units. Not that much longer than a DA*16-50 but much wider in diameter.
The 28-105 is a nice compromise carry about size. If it proves to be of the same optical standard as the DA16-85 it could be a good travel lens. I reckon a K-1 plus the 24-70 would get heavy in the backpack after a few hours walkabout. With the shallower depth of field for a given aperture and better high ISO performance of full frame, the smaller apertures of the 28-105 are less of a hindrance than the same specifications used on APS-C.
Had a play with the 645Z as well. You know that has a big mirror lurking within it. Sound is not harsh but it does take some time to go thru its motions!